Honestly it's hard to gain 20-30 pounds of muscle without gaining fat, I'd say almost impossible. On a good year, with good genetics, you might gain 5-10 pounds of muscle, but I would say don't worry as much about gaining a little extra fat with it. It would be too hard to monitor every inch of muscle gain and too hard to know exactly how many calories your body needs to gain it without gaining fat. When I started I was 170 at 6'2" and I just ate like a madman.
I probably gained about 10 pounds the first year and my goal was to get to 200 pounds. Well, 8 years later, I'm 252 and still climbing although it's very hard to gain muscle mass now a days. It took me over 3 years to get from 240 to 250 the hard way.
So my advice is to keep at it, don't worry so much about the fat gain because it's pretty much inevitable if you plan on gaining 20-30 pounds of muscle. You can always shed off excess poundage later on. Happy lifting.